[PATCH] rules.pl: Fix SNAT over VPN.

[PATCH] rules.pl: Fix SNAT over VPN.

[Stefan Schantl]

[-- Attachment #1: Type: text/plain, Size: 1930 bytes --]

This commit adds flags which will are applied if SNAT should be used on
the red address or any configured alias.

They prevent doing the SNAT when tranismitting packet through a VPN over the red interface.

Fixes #12162.

Signed-off-by: Stefan Schantl <stefan.schantl(a)ipfire.org>
---
 config/firewall/rules.pl | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/config/firewall/rules.pl b/config/firewall/rules.pl
index 86db47367..6129af861 100644
--- a/config/firewall/rules.pl
+++ b/config/firewall/rules.pl
@@ -479,16 +479,31 @@ sub buildrules {
 
 						# Source NAT
 						} elsif ($NAT_MODE eq "SNAT") {
+							my @snat_options = ( "-m", "policy", "--dir", "out", "--pol", "none" );
 							my @nat_options = @options;
 
+							# Get addresses for the configured firewall interfaces.
+							my @local_addresses = &fwlib::get_internal_firewall_ip_addresses(1);
+
+							# Check if the nat_address is one of the local addresses.
+							foreach my $local_address (@local_addresses) {
+								if ($nat_address eq $local_address) {
+									# Clear SNAT options.
+									@snat_options = ();
+
+									# Finish loop.
+									last;
+								}
+							}
+
 							push(@nat_options, @destination_intf_options);
 							push(@nat_options, @source_options);
 							push(@nat_options, @destination_options);
 
 							if ($LOG) {
-								run("$IPTABLES -t nat -A $CHAIN_NAT_SOURCE @nat_options @log_limit_options -j LOG --log-prefix 'SNAT '");
+								run("$IPTABLES -t nat -A $CHAIN_NAT_SOURCE @nat_options @snat_options @log_limit_options -j LOG --log-prefix 'SNAT '");
 							}
-							run("$IPTABLES -t nat -A $CHAIN_NAT_SOURCE @nat_options -j SNAT --to-source $nat_address");
+							run("$IPTABLES -t nat -A $CHAIN_NAT_SOURCE @nat_options @snat_options -j SNAT --to-source $nat_address");
 						}
 					}
 
-- 
2.25.0

Re: [PATCH] rules.pl: Fix SNAT over VPN.

[Michael Tremer]

[-- Attachment #1: Type: text/plain, Size: 2345 bytes --]

Hello,

I just tested this patch on our main firewall in Hanover and the problem is resolved.

It is not the most beautiful piece of code, but it does the job.

-Michael

Tested-by: Michael Tremer <michael.tremer(a)ipfire.org>

> On 20 Feb 2020, at 16:24, Stefan Schantl <stefan.schantl(a)ipfire.org> wrote:
> 
> This commit adds flags which will are applied if SNAT should be used on
> the red address or any configured alias.
> 
> They prevent doing the SNAT when tranismitting packet through a VPN over the red interface.
> 
> Fixes #12162.
> 
> Signed-off-by: Stefan Schantl <stefan.schantl(a)ipfire.org>
> ---
> config/firewall/rules.pl | 19 +++++++++++++++++--
> 1 file changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/config/firewall/rules.pl b/config/firewall/rules.pl
> index 86db47367..6129af861 100644
> --- a/config/firewall/rules.pl
> +++ b/config/firewall/rules.pl
> @@ -479,16 +479,31 @@ sub buildrules {
> 
> 						# Source NAT
> 						} elsif ($NAT_MODE eq "SNAT") {
> +							my @snat_options = ( "-m", "policy", "--dir", "out", "--pol", "none" );
> 							my @nat_options = @options;
> 
> +							# Get addresses for the configured firewall interfaces.
> +							my @local_addresses = &fwlib::get_internal_firewall_ip_addresses(1);
> +
> +							# Check if the nat_address is one of the local addresses.
> +							foreach my $local_address (@local_addresses) {
> +								if ($nat_address eq $local_address) {
> +									# Clear SNAT options.
> +									@snat_options = ();
> +
> +									# Finish loop.
> +									last;
> +								}
> +							}
> +
> 							push(@nat_options, @destination_intf_options);
> 							push(@nat_options, @source_options);
> 							push(@nat_options, @destination_options);
> 
> 							if ($LOG) {
> -								run("$IPTABLES -t nat -A $CHAIN_NAT_SOURCE @nat_options @log_limit_options -j LOG --log-prefix 'SNAT '");
> +								run("$IPTABLES -t nat -A $CHAIN_NAT_SOURCE @nat_options @snat_options @log_limit_options -j LOG --log-prefix 'SNAT '");
> 							}
> -							run("$IPTABLES -t nat -A $CHAIN_NAT_SOURCE @nat_options -j SNAT --to-source $nat_address");
> +							run("$IPTABLES -t nat -A $CHAIN_NAT_SOURCE @nat_options @snat_options -j SNAT --to-source $nat_address");
> 						}
> 					}
> 
> -- 
> 2.25.0
>